Chapter_14IM - Chapter 14 Chemical Equilibrium This is the...

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Chapter 14 Chemical Equilibrium This is the first of several chapters that deals with the concepts of chemical equilibrium. The concept of chemical equilibrium seems to be a difficult topic for many students. Students commonly need several different applications of the topic before finally grasping the subject. Upon completion of this chapter, your students should be able to: 1. Describe chemical equilibrium using the terms forward and reverse reactions and dynamic process. 2. Write the equilibrium constant in terms of the equilibrium concentration of products and reactants and their respective stoichiometric coefficients for both homogenous and heterogeneous equilibria. 3. Express the relationship between K p and K c . 4. Determine equilibrium constant given equilibrium concentration data. 5. Demonstrate that if a reaction can be expressed as the sum of two or more reactions, the equilibrium constant for the overall reaction is given by the product of the equilibrium constants of the individual reactions. 6. Relate equilibrium constant to rate constants from chemical kinetics. 7. Describe the relationship between reaction quotient and equilibrium constant and predict the direction a reaction will proceed to reach equilibrium. 8. Use the concepts of equilibrium to determine concentration of all species in a solution. 9. Use Le Chátelier’s Principle to describe how changing concentration, volume, pressure, or temperature will shift the reaction so that equilibrium will be maintained. 10. Describe the effect of a catalyst has on equilibrium concentrations. Section 14.1 The Concept of Equilibrium and the Equilibrium Constant In Chapter 13, we discussed how the rate of a chemical reaction For a reaction A B can be described as: rate=-∆[A]/ ∆t
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where [A] is the concentration of A, and ∆[A]/ ∆t is the instantaneous change in the concentration of A with respect to time. In this chapter we introduce the concept of equilibrium which can be expressed as −∆[A]/ ∆t =∆[B]/ ∆t =0 for the reaction A ↔ B (Point out the difference of arrow for the tow reactions). Concentration of A and B are not changing with time. Students frequently confuse that the concentrations of products are not equal, but rate is equal. The dynamic nature of equilibrium can be explained in following way: In Chapter 13 we discussed using isotopes to follow chemical reactions and to assist in describing reaction mechanisms. Similar studies can be done with equilibrium systems. For example, in Table 14.1, it is pointed out that the ratio of [NO 2 ] 2 /[N 2 O 4 ] at 25 o C is 4.65 x 10 -3 . It can be difficult for students to understand that at equilibrium NO 2 is being converted to N 2 O 4 and N 2 O 4 is in turn being converted to NO 2. If we were to start with NO
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This note was uploaded on 02/08/2012 for the course CHEM 161 taught by Professor Shaklovich during the Spring '10 term at Harvard.

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Chapter_14IM - Chapter 14 Chemical Equilibrium This is the...

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